20260515 cse dominance trick

[prozacchiwawa]

Note

Medium Risk
Changes optimizer semantics for conditional CSE hoisting; incorrect dominance logic could alter compiled program behavior, though behavior is gated by dialect and legacy paths are preserved.

Overview
Fixes common subexpression elimination when repeated expressions sit inside nested if/i branches: the optimizer could treat a subexpression as safe to hoist even when a deeper conditional reused it without true dominance.

Adds dialect flag cse_dominance on AcceptedDialect (off for all *standard-cl-* includes; compile_module turns it on whenever stepping is set, alongside existing module dialect bumps). cse_is_covering now takes CompilerOpts and, when the flag is enabled, recursively rejects coverage if any downstream condition overlapping the CSE is not itself covered; the prior path-overlap check remains when the flag is false.

CSE entry points (cse_optimize_bodyform, cse_classify_by_conditions, Strategy23 frontend) thread opts through. Regression coverage: resources/tests/cse-complex-4.clsp and test_cse_tricky_2; existing tests pin cse_dominance: false where they assert legacy behavior.

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